Electrical safety interlocking system



Feb. 22, 1949. J. B. GROVER ELECTRICAL SAFETY INTERLOCKING SYSTEM Filed June 30, 1945 V INVENTOR.

James 5. Gro ver ATTOR/VEY Patented Feb. 22, 1949 ELECTRICAL SAFETY INTERLOCKING SYSTEM James B. Grover, New York, N. Y.

Application June 30, 1945, Serial No. 602,632

(Granted under the act of March 3, 1883, as amended April 30, 1928; 370 0. G. 757) 7 Claims.

The present invention concerns an electrical interlock for preventing an electrical circuit from being connected with a source of electrical power when short-circuit condition-s exist, and particularly concerns an electrically operated mechanical interlock for use in conjunction with circuit breakers on feeder lines whereby the circuit breakers cannot be closed when short-circuit conditions exist.

It is customary in providing shore-to-ship electrical power at dry docks and other servicing facilities for ships, to arrange banks of multiple female outlets at convenient points along the dry dock. These outlets are connected by feeder lines to remote substations capable of supplying either alternating or direct current. Male plug and portable extension cable assemblies are used for delivering power from the dry dock outlets to the desired points aboard ship. A usual arrangement, for example, provides female outlets of 400 ampere capacity and capable of supplying 4A0 volt, three-phase alternating current or 250 volt di rect current depending upon the requirements of the ship to be serviced, and for this purpose three-wire type feeders are used to connect each outlet with the source of power at the substation.

In order that either alternating current or direct current can be supplied to the outlets, the end-s of each set of three-wire feeders remote from the outlets and located in the substation are connected to the terminals of a three-pole double-throw switch which can be closed upon power lines from either a source of alternating current such as a main supply transformer or from a source of direct current such as a motor-generator set. Circuit breakers are provided in the 1 power lines leading both to the alternating-current source and the direct-current source to open the circuit upon dangerous loading or short circuiting of the system.

When the feeder lines are connected at the substation to an alternating-current source, the three feeder lines to any outlet carry three-phase current and each dry-dock outlet is an indeoutlet. This system for electrically connecting 2 together the three-wire feeders for transmitting direct current is advantageous since all three feeder wires leading to any outlet are used for carrying current whereas if the three feeder wires to any outlet were arranged to provide one posi-.

tive wire, one negative wire and one dead wire, one-third of the feeder wires would be dead and result in ineificient use of the feeders.

Since insertion of a male direct-current plug in any outlet electrically connects together the three feeder lines to such outlet, inadvertent switching at the remote substation from direct current to alternating current with a male direct current plug in an outlet results in a short circuit. Such a mistake can occur due to the fact that the substation where switching takes place is located at a point remote from the outlets so that the substation operator can be unaware of the fact that an outlet is short circuited by a male direct-current plug. Furthermore, the chance of mistake is increased by use of inexperienced personnel to operate electrical equipment at the dry dock. Clearly the possibility of such a mistake con-stitutes a potential hazard which can result in serious injury to personnel, damage to electrical equipment and delay necessitated in repairing such damage. I

The present invention provides a safety device ior automatically preventing the substation operator from closing the circuit to connect the feeder lines to a source of alternating current when short-circuit conditions exist in the feeder line or at the outlet. The safety device embodies a shunt or by-pass circuit connected across the substation switches from the alternating-current power lines to the feeder lines so that current flows in the shunt or by-pass circuit when shortcircuit conditions exist in'the feeders, and electrical means responsive to such current flow are provided for actuating a mechanical interlock which secures the alternating-current circuit breakers against actuation into closed position.

If desired, an analagous electrically operated interlock can be provided to prevent closing of the direct-current circuit breakers when short circuit conditions exist in the direct-current wiring system.

An object of the invention is to provide electrically operative means for preventing the circuit breaker in a system from being closed when short-circuit conditions exist.

Another object of the invention is to provide electrically operative means for opening the circuit breaker in a system when a short circuit occurs and means for automatically preventing the circuit breaker from being closed so long as short circuit conditions continue to exist.

Another object of the invention is to provide a system of multiple feeder lines adapted for connecting a direct-Fluent source to an outlet with said feeder lines connected together, means for alternatelyconnecting therfeeder lines to a source of alternating current whereby the feeder lines are adapted to be disconnected from each other, and an automatic interlock for preventing the alternating-current circuit from being closed while the feeder lines are connected, together.

Further objects and advantages of this invention, as well as its construction, arrangement and operation, will be apparent from the following description and claims in connection with the accompanying drawings, in which, the single figure is a diagrammatic showing of a preferred form of the invention.

A pair of outlets II and I2 for servicing electrical equipment are adapted for location to gether at the edge of a dry dock or other facility for servicing ships. Outlet II is provided with contacts I3, I4 and I5, connected by means of a. set of three feeder lines 15, ll and it? with contacts I9, 2.0 and 2| of a three-pole doublethrow switch 22 adapted for location in a substation at a point remote from the dry dock where outlet H is located. Outlet 2 is provided with contacts 23, 2d and 25, connected by means of a set of three feeder lines 28, 27 and 28 with contacts 29, 30 and 3| of a three-pole doublethrow switch 32 adapted for location adjacent switch 22 in the substation. ,Switches 22 and 32 are locked for movement together by a mechanical tie rod 32a. 7 Contacts 33, 34 and 35 on one side of switch 22 are connected through circuit breakers 3t, 31 and 38 and through jumper lines 39, cc and M to a common direct-current bus bar 2, that in turn is connected by means of a power line it with one terminal of a source of direct current (not shown) such as a motor-generator set. Contacts 44, 45 and 46 on one side of switch 32 are connected through circuit breakers 4?, t8, 5% and through jumper lines 58, SI and'52 to a common direct-current bus bar 53 that in turn is connected by a power line 54 to the other terminal of the direct-current source. A third bus bar 55 can be provided and connected by means of a power line 56 to the direct-current source for auxiliary use.

With switch 22 closed upon contacts 33, 3t and 35, the three feeder lines it, ll and 58 are all of :the same polarity since the lines are connected to the common bus bar 42 and power line 43. Outlet I l, therefore, is of only one polarity. Simultaneous closing of switch 32 through the medium of tie rod SZaupon contacts $6, $5 and 4'6 causes the three feeder lines 23, 2-1 and 28 to connect with .bus bar 53 and power line 5 3 which is of opposite polarity tothe three feeder lines It, I! and 8. Outlet I-2,.theref ore, is, of a polarity oppositeto outlet II. In direct-current operation, therefore, outletsIl and 52 are used together in a pair, one of the outlets providing positive polarity and the other outlet providing negative polarity. The direct-current male plugs (not shown) used for insertion in outlets ii and I2 are designed to-connect contacts 53, id and I5 or contacts 23, 24 and 25 together electrically during direct-current.operation. This arrangement of feeders whereby during direct-current operation all three of the feeder lines It, i! and I8 are of one polarity and are connected to ether current to outlets at outlet II while all three of feeder lines 25, 27 and 28 are of the opposite polarity and are connected together at outlet I2, is provided to afford most efficient use of the feeder lines since by this arrangement all three of the feeder lines leading to a particular outlet are carrying current, whereas if one feeder line such as was carrying current of one polarity and the second feeder line I! was carrying current of opposite polarity, the third feeder line I8 would not be carrying current, thus resulting in inefficient use of the feeder lines.

In the wiring system for providing alternating II and I2 contacts 57, 5,8 and 59 of switch 22 are connected through circuit breakers 6G, 6! and 62 and through jumper lines 53, 6-5 and $5 to alternating-current bus bars 86, El and E8 in turn are connected through power lines 5%, l9 and H to a source of alternating current (not shown) such as a main supply transformer. Circuit breakers 56, Si and 82 canbe of the type to provide time delay and instane taneous trip features for giving overload and short-circuit protection respectively when the system is in alternating-current operation for separate circuit. breakers for this purpose can be provided. If desired, three-phase alternatin current can be provided from the source. Contacts l2, l3 and Hi of switch 32 are connected through circuit breakers l5, l5 and fl and through jumper lines I8, 19 and 8i} to alternatingcurrent bus bars 66, 61 and 68. Circuit breakers it and ll are similar to circuit breakers 55, iii and S2 and can provide overload and shortcircuit protection during alternating-current operation or separate circuit breakers for this purpose can be provided. 7 i

When switch 22 is closed upon contacts 51., 58 and 59, the three feeder lines I5, I! and !8 are arranged to carry three-phase alternating current and outlet I I operates independently of outlet I2. Simultaneously closing of switch 32 through the medium of tie rod 32a upon contacts T52, 13 and M, causes the three feeder lines 25, 2'! and 23 to carry three-phase alternating current and outlet I2 operates independently of outlet II'. Therefore, in alternating-current operation outlets H and 82 are used independently and are not used in pairs as is the case with directcurrent operation. The alternating-current male plugs (not shown) for insertion in outlets H. and

I2 are designed not to connect contacts I3, I l and IE or contacts 23, 24 and 25 together electrically and in this respect differ from the directcurrent male plugs.

Since the direct-current male plugs are designed to connect together the contacts in an. outlet, for example, contacts l3, I4 and I5 of outlet II, ifa male direct-current plug is inserted in outlet ii when switch22 is closed upon contacts 51, 58 and 59 to provide alternating current, short circuit conditions exist. Since switch22 gisadapted for location in a substation remote from outlet II, switch 22 might inadvertently be closed into alternating-current position whilea male directcurrent plug is inserted in outlet II to create short-circuit conditions. To prevent this from happening, the following automatic interlock is provided for insuring that circuit breakers '60, 8i and 62, and circuit breakers 15, 1.6 and I1 cannot be closed while such short-circuit conditions prevail.

A shunt or by-pass circuit is provided including a conductor 8I, connected at one end to alternating-current 'bus bar 61, and connected through a current-limiting resistance 82 and fuse 83 to one end of transformer primary 84, the other end of which is connected by conductor 85 through fuse 88 and current-limiting resistance 81 to alternating current bus bar 68. Transformer secondary winding 88 is connected at one end by conductor 88 to terminal 90 of a double-pole double-throw switch 9|, the other terminal 92 of which is connected by conductor 93 through a clapper-type relay 94 to the other end of transformer secondary 88. Switch 9| is provided on one side with contacts 96 and 91 connected together at 98. On the other side, switch 9| is provided with contacts 99 and I00. Contact 99 is connected by conductor to one end of a transformer secondary I02 the other end of which is connected by conductor I03 to contact I00. One end of transformer primary I04 is connected by conductor I05 through a fuse I06 and a current-limiting resistor I01 to contact 3| of switch 32. The other end of transformer primary I04 is connected by a conductor I08 through fuse I09 and current-limiting resistor III) to contact 30 of switch 32.

A second shunt circuit is provided including a conductor 8|, connected at one end to conductor 8| and at its other end connected to one end of transformer primary 84, the other end of which is connected by conductor 85 to conductor 85. Transformer secondary winding 88 is connected at one end by conductor 89 to terminal 90 of a double-pole double-throw switch 9|, the other terminal 92 of which is connected by conductor 93' through a clapper type relay 94 to the other end of transformer secondary 88. Switch 9| is provided on one side with contacts 96 and 91 connected together at 98'. On the other side, switch 9| is provided with contacts 99' and I00. Contact 89 is connected by conductor IOI to one end of a transformer secondary I02 the other end of which is connected by conductor I03 to contact I00. One end of transformer primary I04 is connected by conductor I05 through a fuse I08 and a current-limiting resistor I01 to contact 2| of switch 22. The other end of transformer primary I04 is connected by a conductor I08 through fuse I09 and current limiting resistor M0 to contact of switch 22.

Adjacent clapper-type relay 94 and adapted for actuation thereby is a relay switch |I3 having a contact 4 connected through a conductor II5 to one terminal of a suitable source of current (not shown). The other contact N8 of switch I I3 is connected by a conductor I I1 through a signal lamp II 8 to a trip coil H9 and by a conductor I20 to the other terminal of the current source (not shown). An alarm signal I2I is connected across lines III and I20. Trip coil H9 is provided with a laminated plunger I22 connected to circuit breaker IT. A mechanical tie bar I23 locks circuit breakers 80, BI, 62 and I5, I0 and IT for movement together under the influence of trip coil H8 and laminated plunger I22.

Adjacent clapper type relay 94' and adapted for actuation thereby is a relay switch I I3 having a contact II4 connected through a conductor II5 to conductor H5. The other contact N8 of switch H3 is connected by a conductor III to conductor III.

Operation of the device is as follows. Assume switches 22 and 32 to be in open position as shown in the figiu'e and assume that short-circuit conditions exist, for example, between feeder lines 2'! and 28 by virtue of a male direct-current plug being inserted in outlet I2, or for other reasons.

' It is necessary under such conditions that the alternating circuit be prevented from being closed. This is accomplished by automatic locking in open-circuit position of circuit breakers 60, BI, 82 and I5, I6 and I1 under the influence of trip coil H9 in the following manner. Switches 9| and 9| during normal operation are closed upon contacts 98 and I00 and contacts 99 and I00 respectively. Under such conditions if a short circuit exists as described between feeder lines 21 and 28, the impedence of transformer I04 is reduced almost to short circuit impedence so that current flows through conductors 8| and 85, transformer windings 84 and 88, clapper type relay 94, switch 9|, transformer windings I02 and I04, conductors I05 and I08, feeder lines 21 and 28 and the short circuiting male plug in outlet I2. Such current flow actuates clapper type relay 94 to close switch I I3 so that current flows through conductors II 5 and I20 and trip coil II9. Trip coil 9 is energized to cause reciprocation of laminated plunger I 22 which through mechanical tie rod I23 locks circuit breakers 60, BI, 02 and I5, I6 and 11 open until short-circuit conditions are eliminated. At the same time, lamp H8 is illuminated to give a visual indication that short-circuit conditions exist and alarm I2I is activated to give a further indication that short-circuit conditions exist.

In a similar manner if switches 22 and 32 are in open position and short-circuit conditions exist, for example, between feeder lines I1 and I8 by virtue of a male direct-current plu being inserted in outlet II or for other reasons, circuit breakers 80, GI, 82 and I5, I5 and II are automatically locked in open circuit position as follows. The short circuit described reduces the impedance of transformer I04 so that current flows through conductors 8|" and 85, transformer windings 84 and 88, clapper type relay 94, switch 9|, transformer windings I02 and I04, conductors I05 and I08, feeder lines I1 and I8 and the short circuiting male plug in outlet II. Such current flow actuates clapper type relay 94 to close switch II3' so that current flows through conductors H5, H5, III, II! and I20 and trip coil H9. Trip coil H9 is energized to cause reciprocation of laminated plunger I22 which through mechanical tie rod I23 locks circuit breakers 00, GI, 62 and I5, I6 and I! open until short-circuit conditions are eliminated. At the same time, lamp H8 is illuminated to give a visual indication that short-circuit conditions exist and alarm |2I is activated to give a further indication that short-circuit conditions exist.

Thus, should a male direct current plug be inadvertently inserted in either receptacle II or receptacle I2, circuit breakers 60, BI, 52 and I5, I8 and H are locked automatically in open circuit position.

However, assume switches 22 and 32 to be in open position as shown in the figure and conditions as described in the preceding paragraph, but assume that no short circuit conditions exist either at outlets II and I2 or in feeder lines I8, I], I8 or 28. 21 and 28. Under such conditions current does not flow through the shunt circuit including conductors BI, 85, I05 and I08 since open circuit conditions exist at contacts 30 and 3| of switch 32. Also under such conditions current does not flow through the shunt circuit including conductors 8|, 85, I05 and I 08 since open circuit conditions exist at contacts 20 and 2| of switch 22. The impedances of secondary transformer windings I 04 and I04 under these conditions are high enough to prevent'current .ilow. Therefore; tripicoil -l:l 9:is notenergizedand the alternating current circuit breakers '60, El, 692 and 15, 1.8 and'l-l are'not locked inopen position but can be closed to condition the circuit for alternating-current operation when switches -ikfiand -32-areclosed on contactsSL-EB, 59 and lid-and l4 respectively.

Assuming switches 22 and 32 are closed for direct-current operation upon contacts 33, .34, SE-and lL-tS-and es, respectively, with switch 9| closed upon contactstiland IE8, and with switch :9!" closedupon contacts 99' and 1%, and that direct-currentmale plugs are inserted in outlets H and i2 for-operating direct-current electrical -equipment, the alternating current circuit :breakers t n-iii, 52 and 15,16 and ll-are locked -in open circuit position. I-his is true since contacts 1.9, so and 2-! of switch 22 are electrically interconnected-both by presence of a direct currentunale plug in outlet H and connection of jumperlinesi ic and ti to a common bus bar :4'Z,-and in the same manner contacts 29, 3!] and ill of switch 32 are electrically interconnected. Because contacts 28 and 2! of switch 22 are interconnected and contactsafl and 3! of switch 32 -are interconnected, current flows through the shunt or by-pass circuit which includes conductors 8!, 85, N35 and 688 and also through the shunt .or-by-passcircuit which includes conductors ili'rllfi', Hi5 and H18 whereby trip coil H9 is energized to lock alternating-current circuit breakers MAL-52 and 15,16 and T! in open-cir- Jcuit position.

Assuming now that all direct-current male plugs are removed from outlets H and 1.2 and that-ieederlines H5, ll, 18 and '26, 2'! and 28 are otherwise free from short circuits and vfurther that switch ill is closed upon contacts 99 and IE9, and switch 9-! is closed upon contacts 99 and 4%, the system can be conditioned :for alternating-current operation by closing switches 22 and 352 upon-contacts 51, 58,59 and l2, l3 and i4 respectively-and closing circuit breakers 60, 6!, :and l5, l5 and Ti. Under such conditions equal potential exists at busbarfil andcontact:

3c .of switchtz, also equal potential exists at bus -bar EBandcontact 3i. Inasmuch as transformer secondaries iil and i'LlZare connected in opposed polarity, only a small magnetizingcurrent flows in' thecircuit including'conductors :8 l 85 and M51.

.andlilfi, and such small current isnot sufficient to-energizerelay at. For similar reasons,-only a small magnetizing current flows in .the circuit includingconductors ill, 85 and H35, 508 and such small current is not sufiicient to energize,

relay sea Therefore, trip coil I i9 is not energized and the alternating-current circuit-breakers $315!, .62 and 1.5, Iii-and T! are not locked in open position.

By the arrangement described, continuous,

automatic guarding of the electrical system against improper operation is provided. When the system is in closed-circuit condition and operating either with alternating current or direct current an automatic guard against overload and short-circuit operation can be provided by use of conventional alternating current and direct-current breakers respectively of the type which have time delay and instantaneous trip .features.

Should short-circuit conditions arise when the -nating-current circuit repair work is beingperformed on outlets H and i2, switch 9! isclosed upon contacts and 197.

Under such conditions, connection *98 provides a short circuit whereby current fiowsthroughconductors 8! and 85, transformer windings 84-and 83, andclapper type relay Site close switch 3 and cause trip coil l E9 to be energized and lock alternating-current circuit breakers 69, 51, 6-2 and '15, i6 and ll in open position. In like manner switch 95' can be closed upon contacts 96 andtil to energize trip'coil "I I9.

It is to be understood that a direct-current interlock analogous to the alternating-current interlock can be provided for locking the-directcurrent circuit breakers against closing when =short-circuit direct-current conditions exist, if desired. In such case conductors analogous .to 8! and can be conn cted to bus bars 42 and 53, respectively. A conductor analogous to conductor 505 can be connected to contact 29,30 or 35 of switch 32 and a conductor analogous to conductor i653 can be connected to contact i9, 253 orzi oiswitchZZ. Transformers'are omitted since such-a shunt circuit is direct current 019- erated.

While for purposes of illustration there .have been disclosed only two outlets, ii andlZ, with corresponding feeder lines, it is understoodthat more outlets and corresponding feederlines can be used as required. Furthermore, whilealthreewire three-phase alternating-current system is disclosed and a three-wire direct-current system is disclosed, any desired type of alternating-currentsystem with suitable number of wires .can

- be used and any desired direct-current wiring system may be used.

The shunt circuit providing the automatic interlocking action isillustrated asbeing-connected to only two wires .ofa three-wire system of feeders, but it is understood that the shuntcircuit can be arranged for connection to any suitable combination of feeders including all or the feeders if desired.

It is to be understood that various modifications and changes can be made in this invention without departing ifrom the spirit and scope thereof asset forthin the appended claims.

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental .purposes without thepayment-of any royalties thereon or therefor.

What is claimed is:

1. In an electrical system, a line adaptedto connect a power-source and aload, circuit breaking means in said line adapted to be disposed in open-circuit or closed-circuit relation, and a bypass circuit connected across the circuit breaking means, and including means electrically 'energized during existence of a short-circuit condition at the load to retain said circuit breaking means in open-circuit relation.

2. In an electrical system, aline adapted to connect a power source and a load,.circuit breaking means in said line adapted to be disposed in open-circuit or closed-circuit relation, and a bypass circuit connected across the circuit breaking means and including electromagnetic means responsive to flow of current in the bypass circuit upon existence of ashort circuit .condition at the load for retaining said circuitbreaking means in open-circuit relation.

3.]In an electrical system, a line adapted etc connect a power source and a load, circuit breaking means in said line adapted to be disposed in open-circuit or closed-circuit relation, and a by-pass circuit connected across the circuitbreaking means, a second line adapted to connect a source of power with an electromagnetic device, means interconnecting said electromagnetic device and said circuit breaking means for retaining the circuit breaking means in open-circuit relation upon flow of current in the second line, a switch in the second line, and electromagnetic means responsive to flow of current in the by-pass circuit during existence of a short circuit condition at the load for closing the switch in the second line to permit flow of current in the second line.

4. In an electrical system, a line adapted to connect a source of power and a load, circuit breaking means in said line adapted to be disposed in open-circuit or closed-circuit relation, and a bypass circuit connected across the circuit-breaking means, said by-pass circuit including a transformer having one winding connected to the power source part of the line and the other winding connected to the load part of the line, and means responsive to flow of current in the by-pass circuit during existence of a short-circuit condition at the load to retain said circuit-breaking means in open-circuit relation.

5. In an electrical system, a line adapted to connect a source of power and a load, circuit breaking means in said line adapted to be disposed in open-circuit r closed-circuit relation, a by-pass circuit connected across the circuit-breaking means including a first transformer and a second transformer, the primary winding of the first transformer being connected to the power source part of the line, the primary winding of the second transformer being connected to the load part of the line, the secondary windings of the transformers being connected in series in opposed relation, and means responsive to flow of current in the bypass circuit during existence of a short-circuit condition at the load to retain said circuit breaking means in open-circuit relation.

6. In an electrical system, a line adapted to connect a power source and a load, circuit breaking means in said line adapted to be disposed in opencircuit or closed-circuit relation, and a by-pass circuit connected across the circuit breaking means including a first transformer and a second transformer, the primary winding of the first transformer being connected to the power source part of the line, the primary windin of the second transformer being connected to the load part of the line, the secondary windings of the transformers being connected in series in opposed relation, a second line adapted to connect a second source of power with an electromagnetic device for retaining the circuit-breaking means in open circuit relation upon flow of current in the second line, a switch in the second line, and a relay responsive to flow of current in the by-pass circuit during existence of a short circuit condition at the load for closing the switch in the second line to permit flow of current in the second line.

7. In an electrical system, a multiple-pole double throw switch adapted for connection to a load, a first line adapted to connect a first set of switch poles with a source of potential difierence, a second line adapted to connect a second set of switch poles with a common conductor so that said switch can connect the load with the source of potential difference or the common conductor, circuit breaking means in said first line adapted to be disposed in open-circuit or closed-circuit relation, and a by-pass circuit connected across the circuit breaking means, and including means electrically energized to retain said circuit breaking means in open circuit relation when the load is connected to the common conductor or when a short-circuit condition exists at the load.

JAMES B. GROVER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 529,265 Harrison Dec. 13, 1894 Re. 13,856 Raney Dec. 29, 1914 1,435,255 Puxon Dec. 14, 1922 

